They are backed up by a Swedish aquirer/processing company called Samport.
http://www.samport.com/
The stamps on the mail from Zambaio also show that their mail is send from Sweden.
Some sites on the same IP Address/server as the main Zambaio website:
Gcbtech.com - Game Control Board
Io-movies.com - Movie download site (mainstream)
Iobilling.com / Iocharge.com / Iohelp.com